1. Field of the Invention
The present invention relates to a data communication apparatus which transmits or receives image data, code data or the like.
2. Description of the Prior Art
Hitherto, data communication apparatus of this kind, for example, facsimile apparatuses generally have been provided with an automatic reception mode whereby an original image is received without the information of an operator and a manual reception mode whereby the original image is received through operator intervention. The manual reception mode includes an ordinary manual reception mode whereby an operator is present on the transmission side and also a manual polling reception mode whereby an original set on the transmission side is automatically read on the transmission side by accesssing from the reception side to the transmission side without operator intervention on the transmission side and this read image is received on the reception side.
On one hand, a facsimile apparatus generally transmits its own communication mode as an initial identification signal to an apparatus of the called party side in order to set a common communication mode, such as the same communication procedure, communication standard or the like.
In the manual polling reception mode, initial identification signals are mutually transmitted from both of the transmission and reception sides, so that there is a case where the initial identification signals collide with each other on the line and both transmission and reception sides cannot identify the mutual initial identification signals and the polling communication is not performed. Further, there is a drawback such that even if the polling is executed, it takes a long time for the preparation since the signals collide with each other. FIG. 1 shows a typical practical example whereby in case of performing the polling between conventional facsimile apparatuses, the initial identification signals collide with each other and the polling is not executed.
In FIG. 1, various kinds of signals are signals based on the CCITT recommendation T30. A reference numeral 1 denotes a called station identification (CED) signal; 2 and 6, preambles which are transmitted prior to the transmission of a binary signal; 3 and 7, nonstandard function (NSF) signals; 4, a called terminal identification (CSI) signal; and 5 and 8, digital identification (DIS) signals. In FIG. 1, subsequent to the CED signal, the NSF, CSI and DIS signals are transmitted on the automatic reception side. Thereafter, the binary signal is received for three seconds on the same side. When signals (a nonstandard function setting (NSS) signal, a transmitting terminal identification (TSI) signal and a digital command (DCS) signal) in the group of the DCS signal are received from the facsimile apparatus on the calling party side, a training check (TCF) signal is then received and thereafter image information is received. On the other hand, when signals (a nonstandard function command (NSC) signal, a calling station identification (CIG) signal, a digital transmission command is effected. A (DTC) signal in the group of the DTC signal are received from the facsimile apparatus on the called party side, the signals in the DCS group are transmitted and thereafter the polling transmission of the image information is performed. However, as shown in FIG. 1, no binary signal is transmitted from the facsimile apparatus on the called party side when the binary signal is to be received, so that the NSF, CSI and DIS signals are transmitted after an expiration of three seconds. Thereafter, the binary signal is received for three seconds. The foregoing operation is repeated until the initial identification time (for instance, 35 seconds) elapses, and the error end is caused. On the other hand, when the operator presses a start button after becoming aware of the CED signal, the facsimile apparatus on the manual reception side starts the transmission of the initial identification signal. The facsimile apparatus on the manual reception side does not transmit the CSI signal. In this case, the NSF and DIS signals are first transmitted and thereafter the binary signal is received for 4.5 seconds. When the signals in the DCS group are received from the facsimile apparatus on the calling party side, the training check (TCS) signal is received, thereafter the image information is received. On the other hand, when the NSF signal and DIS signal (bit 9 in a facsimile information field (FIF) is 1, namely, there is a transmitting original) are received from the facsimile apparatus on the calling party side (the CSI signal may not be received), the signals in the DTC group are transmitted and thereafter the (polling reception of the image information is performed. However, as shown in FIG. 1, the binary signal subsequent to the preamble is not transmitted from the facsimile apparatus on the calling party side when the binary signal is to be received; consequently, the NSF, CSI and DIS signals are transmitted after an expiration of 4.5 seconds. Thereafter, the binary signal is received for 4.5 seconds. The foregoing operation is repeated until the initial identification time (e.g., 35 second) elapses, and the error end is caused. In the foregoing embodiment, it has been considered the case where the relation of .alpha.=.beta.+1.5 is satisfied when it is assumed that the time of the initial identification signal which is transmitted from the automatic reception side (the time from the start of transmission of the preamble signal until the end of the DIS signal) is .alpha. (seconds.) and the time of the initial identification signal which is transmitted from the manual reception side (the time from the start of transmission of the preamble signal until the end of the DIS signal) is .beta. (seconds). Although the case where .alpha.=.beta.+1.5 is satisfied does not practically occur so frequently, .alpha.&gt;.beta. could occur. Further, in case of the facsimile apparatus having the functions based on the CCITT Recommendation T2 and T3, a ternary signal is transmitted prior to the binary signal, so that the execution of the polling operation becomes more difficult than the case where only the binary signal is transmitted.
On the other hand, in the case where the facsimile apparatus on the calling side is in the manual transmission mode, namely, in case of the ordinary manual reception mode, the transmission side does not transmit any signal until the signals in the DIS group which are transmitted from the facsimile apparatus on the manual reception side are received and after the DIS signals were received, the transmission side transmits the signals in the DCS GROUP. Therefore, the collision of the initial identification signals as in the polling operation does not occur and the ordinary image transmission is executed.